I. Field of the Invention
The present invention relates to a semiconductor device and more particularly a press-packed semi-conductor device with improved positioning and returning means of a semiconductor element with respect to electrode disk members.
II. Description of the Prior Art
A press-packed semiconductor device includes, for example, a power diode whose longitudinal sectional view is shown in FIG. 1. The semiconductor device is provided with an insulating tubular body 1 made of ceramic, a pair of ring-shaped covers 2 and 2' made of for example Kovar (manufactured by Westinghouse Electric Corp.) and hermetically oppositely mounted at both end faces of the tubular body 1, and a pair of electrode disk members 3a and 3c partially and hermetically fitted in both end openings of the ring-shaped covers 2 and 2' coaxially with the insulating tubular body 1. The insulating tubular body 1, the ring-shaped covers 2 and 2', and the electrode disk members 3a and 3c cooperatively make up an hermetic enclosure. A semi-conductor element 4, disposed between the pair of electrode disk members, is press-supported by heat buffer plates 5a and 5c respectively disposed between the semiconductor element 4 and the corresponding electrode disk member 3a or 3c.
As for the semiconductor element 4, a cathode electrode 4c made of Al or Au is provided on one of the main surfaces of the silicon substrate 4b (e.g. the upper surface as viewed in FIG. 1). The other main surface (the lower surface as viewed in FIG. 1) of the silicon substrate 4b is brazed to one of the main surfaces of the heat buffer plate 5a made of Mo or W by means of a brazing layer 4a serving also as an anode electrode. The heat buffer plate 5a is coaxially supported to the inner wall of the insulating tubular body 1 at the peripheral surface of the same by means of a positioning member 6 made of insulating material such as rubber fixed to the inner wall of the insulating tubular body 1. The other main surface of the heat buffer plate 5a is in a press-contact with the anode disk member 3a. The cathode electrode 4c of the semiconductor element 4 is in press-contact with the cathode disk member 3c with the heat buffer plate made of Mo or W interposed between them. Pressure to be applied on the semiconductor element 4 is produced in the electrode disk members 3a and 3c when the enclosure is assembled.
Thus, in the prior semiconductor device, the heat buffer plate 5a is brazed to the semiconductor element 4. In this case, the heat buffer plate 5a is made of Mo or W whose expansion coefficient is very approximate to that of silicon of the semiconductor element. Nevertheless, there is still an expansion coefficient difference between them. Because of this, the silicon substrate 4b and the heat buffer plate 5a operate together like a bimetal. Accordingly, when heated, the silicon substrate 4b and the heat buffer plate 5a are warped. To avoid the warp, a relatively thick plate must be used for the heat buffer plate 5a. Further, in the prior art device, a thermal strain is produced in the brazing process, reducing the breakdown voltage of the semiconductor device. The brazing process is also troublesome and time-consuming.